As it is known by the man skilled in the art and as defined into the 3GPP technical specifications (TS 23.060), the so-called dual transfer mode (or DTM) allows carrying out a packet-switched (PS) signalling procedure through the circuit-switched (CS) domain by means of the GTTP protocol (“GPRS Tunnelling Transport Protocol”). Such a situation notably occurs when a CS connection has been established, for a CS signalling or for a CS voice or data transfer, and GPRS Mobility Management (GMM) procedures or Session Management (SM) procedures need to be carried out in the same time.
When both CS and PS Mobility Management procedures are required (due to a change of area, for instance), these procedures are launched simultaneously starting with the CS procedure first. So, when a CS connection is established, then a PS procedure can be done during the CS connection by means of the GTTP protocol. When the CS procedure is ended, the Circuit Mobility Management (CMM) starts a timer (called T3240) awaiting for the release of the CS connection from the network. So, when the timer T3240 is expired (i.e. after 10 seconds), the CMM aborts the CS connection.
However, the PS procedure might not be completed and it might be still running through GTTP. The CS connection being aborted, the PS procedure cannot continue on CS channels. Therefore in order the PS procedure to continue, GPRS resource allocation procedures must ideally be carried out to establish a temporary block flow (TBF). In uplink (i.e. from the mobile station toward the network), this TBF establishment requires a new access to the network for resource requests, and in both downlink (i.e. from the network toward the mobile station) and uplink, the network has to allocate new resources to the mobile station. These new access and new resource allocation slow down the PS signalling procedures.
Moreover, when the CS connection has been aborted, the Radio Resource entity (RR) may need to perform a re-acquisition of System Information (SI), and possibly a cell reselection. So the above mentioned GPRS resource allocation procedures are delayed until the SI re-acquisition and the possible cell reselection are completed in the Radio Resource entity. This still increases the slowing down of the PS signalling procedures.